Physiological Plasticity of Neural-Crest-Derived Stem Cells in the Adult Mammalian Carotid Body

Abstract

Adult stem cell plasticity, or the ability of somatic stem cells to cross boundaries and differentiate into unrelated cell types, has been a matter of debate in the last decade. Neural-crest-derived stem cells (NCSCs) display a remarkable plasticity during development. Whether adult populations of NCSCs retain this plasticity is largely unknown. Herein, we describe that neural-crest-derived adult carotid body stem cells (CBSCs) are able to undergo endothelial differentiation in addition to their reported role in neurogenesis, contributing to both neurogenic and angiogenic processes taking place in the organ during acclimatization to hypoxia. Moreover, CBSC conversion into vascular cell types is hypoxia inducible factor (HIF) dependent and sensitive to hypoxia-released vascular cytokines such as erythropoietin. Our data highlight a remarkable physiological plasticity in an adult population of tissue-specific stem cells and could have impact on the use of these cells for cell therapy.

Keywords: angiogenesis and neurogenesis; carotid body physiology; hypoxia; neural-crest-derived adult stem cell plasticity and multipotency.

Graphical abstract

Figure 1

CB Stem Cells Contribute to Angiogenesis in Addition to Neurogenesis under Hypoxia (A) Z stack projection picture obtained by confocal microscopy from a CB section of a hypoxic GFAP-cre/floxed LacZ mouse, immunostained with an antibody against β-galactosidase (red) and stained with the endothelial marker GSA I (green). ECs derived from GFAP⁺ type II cells are shown in the enlargements of the boxed areas (arrows). Scale bars, 10 μm. Confocal pictures were taken in sections from two animals per group. (B–E) Examples of X-gal⁺ cells dispersed from the CB of hypoxic GFAP-cre/floxed LacZ mice. The pictures illustrate the appearance of X-gal⁺ ECs (GSA I⁺, B), glomus cells (TH⁺, C), smooth muscle cells (SMA⁺, D), and pericytes (NG2⁺, E). Scale bars, 5 μm. n = 3 independent experiments. (F) Fluorescence confocal microscopy pictures of CB sections from hypoxic GFAP-cre/floxed YFP mouse stained with anti-YFP antibody (green) and rodhamine-conjugated GSA I lectin. Arrows point to double-positive vessels. A higher magnification of the boxed region depicted in (F), showing z axis projection views, is shown in (1). Scale bars, 25 μm. n = 3 animals per experimental group. (G) Picture of ex vivo hypoxic CB preparation stained with GSA I (green) and immunolabeled with an antibody against YFP reporter protein (red). Note the presence of GSA I positive ECs, negative for the reporter protein (white arrowheads). Scale bar, 25 μm. (H and I) Examples of GFAP⁺ cell-derived CD31⁺ ECs, found in CB cell dispersions from both GFAP-cre/floxed YFP (H) and GFAP-cre/floxed LacZ (I) mice. Scale bars, 20 μm. See also Figures S1 and S2.

Figure 2

Single Progenitor Cells Display Multipotency In Vitro (A and C) Bright-field photographs of secondary NS formed from single progenitors derived from enzymatic dispersion of primary NS. Scale bars, 5 μm. (B and D) Immunofluorescence pictures of adherent secondary NS obtained from a single NS-derived progenitor cell (NSPC). Combinations of different cellular markers were tested inside the same colony (Tuj1 [green] and GSA I [red] in B, and TH [green] and vWF [red] in D). Scale bars, 100 μm. B1 and B2 and D1 and D2 show high-magnification images of the areas boxed in (B) and (D). Scale bars, 10 μm, in B1 and B2, and 30 μm, in D1 and D2. n = 4 primary NS cultures. (E) Flow cytometry plot of dispersed rat CB cells transfected with pGFAP-eGFP plasmid. (F) Image representing GFAP⁺ cell enrichment in GFP⁺ cell population sorted out by flow cytometry. Scale bar, 10 μm. (G) Bright-field pictures showing the ability of single-cell plated GFP⁺ cells (1 d) to form NS after 15 days (15 d) in culture. Scale bars, upper panel 10 μm and bottom panel 50 μm. (H) Example of a single-cell-derived NS, containing cells of both neuronal (TH, red) and endothelial (GSA I, green) lineages. Scale bars, 10 μm, in (H), and 5 μm, in inset. (I) Single-cell plating experiment performed using dispersed CB cells from hGFAP-GFP mice. Picture shows an example NS, double positive for neuronal (TH, green) and endothelial (GSA I, red) markers. Scale bar, 50 μm. See also Figure S3.

Figure 3

Vascular Factors Increase CBSC Endothelial Differentiation In Vitro (A) Epifluorescent detection of GSA I (ECs; red) in adherent NS cultured on fibronectin in standard neural crest culture medium without mitogens (CTRL) and supplemented with vascular or neuronal factors. Scale bar, 200 μm. (B) Quantification graph indicating the mean percentage of GSA I⁺ cells among total cells in different culture conditions. Data are represented as the mean ± SEM.; ^∗p ≤ 0.05, ^∗∗p ≤ 0.01; # p ≤ 0.001, one-way ANOVA Newman-Keuls post hoc test compared to CTRL measurement. n = from three to nine independent NS cultures. (C and D) Graphs representing a significant increase in mRNA expression of two classical hypoxia-inducible genes, VEGF (C) and GLUT1 (D). n = 4 independent NS cultures. In vitro hypoxia experiments were performed at 3% O₂. Data are represented as mean ± SEM. (E) RT-PCRs revealing expression of mature endothelial markers in rat liver and in GSA I⁺ cells isolated from CB or adherent NS by flow cytometry. (F) Agarose gel showing TH mRNA amplified by RT-PCR in GSA - cell fraction isolated from adherent NS. Three independent RNA extractions were tested for each gene expression analysis. (G) Binding of FITC-GSA I and uptake of DiI-acetylated LDL (Ac-LDL) in ECs in vitro, visualized by fluorescence microscopy. Nuclei are counterstained with DAPI (blue). Scale bars, 50 μm (top) and 25 μm (bottom). n = 3 NS cultures. See also Figures S3, S4, and S6.

Figure 4

EPO Promotes the Endothelial Differentiation Capacity of CBSCs (A) Immunohistochemistry pictures illustrating the size of TH⁺ neuronal blebs in control and EPO-exposed NS. Scale bar, 50 μm. (B) Quantification of the percentage of TH⁺ cells versus total cells in NS sections, comparing control and EPO-treated NS. Data are represented as the mean ± SEM. No statistical differences were detected by Student’s t test. (C) Immunofluorescence pictures showing presence of EPO receptor (EPOR) on the surface of nestin⁺ progenitors in both NS (upper panels) and CB (lower panels) tissues. Scale bars, 50 μm, in upper panels, and 10 μm, in lower panels. (D) Images displaying EC differentiation within adherent cultures of primary NS in presence of EPO, EPO combined with EPO neutralizing antibody, or EPOR inhibitor (AG490). Scale bar, 50 μm. (E) Quantification graph indicating the mean percentage of GSA I⁺ cells in different culture conditions. Data are represented as the mean ± SEM; ^∗p ≤ 0.05, one-way ANOVA Newman-Keuls post hoc test compared to control measurement (white bar), and #p ≤ 0.05, one-way ANOVA Newman-Keuls post hoc test compared to EPO treated measurement (black bar) (n = 3 cultures). (F) Agarose gel showing the presence of EPO mRNA in hypoxic CB samples. n = 3. (G) Schematic diagram describing the co-culture experiment. (H) Representative western blot detecting EPO in three different hypoxic HUVEC protein extracts. The antibody recognizes in the cell extracts a band of about 38 kDa in concordance with human recombinant EPO (Hu-EPO). (I) Pictures showing EC differentiation, detected by intracellular DiI-Ac-LDL uptake, occurring in NSPCs in different co-culture conditions. Parallel NS cultures without HUVECs served as control (CTRL). Scale bar, 25 μm. (J) Quantification graph showing the percentage of DiI-Ac-LDL⁺ cells detected in different co-culture conditions. Data are represented as the mean ± SEM.; ^∗∗p ≤ 0.01, one-way ANOVA Newman-Keuls post hoc test compared to Ctrl measurement; #p ≤ 0.05, one-way ANOVA Newman-Keuls post hoc test compared to HUVEC co-culture measurement (n = 4 cultures). (K) Histogram representing the significant increase of hematocrit, a typical hypoxia-sensitive EPO-mediated physiological variable, in experimental hypoxic animals (gray bar, n = 5) versus normoxic animals (white bar, n = 4). Consistently, treatment of hypoxic animals with EPOR inhibitor AG490 produced a significant decrease of hematocrit levels (black bar) when compared to hypoxia. In vivo experiments were carried out at 10% O₂. Data are represented as mean ± SEM. (L) Representative microphotographs of X-gal⁺ GSA I⁺ cells observed in dispersed CB from GFAP Cre/floxed LacZ mice exposed to hypoxia for 7 days. Scale bars, 10 μm. (M) Quantification of the percentage of X-gal⁺ GSA I⁺ cells versus total X-gal⁺ cells found in dissociated CBs from GFAP Cre/floxed LacZ mice injected with vehicle (n = 3) or AG490 (n = 3), after 7 days of hypoxic treatment. ^∗∗p ≤ 0.01, Student’s t test compared to vehicle-treated hypoxic animals. Data are represented as mean ± SEM. See also Figures S5 and S6.